Wash the asparagus, remove the hard part.
Cook the asparagus: you can either steam them for 5 minutes and then fry them for 5 minutes, or simply steam them (10 to 15 minutes depending on the size) or simply fry them (also 10 to 15 minutes), as you prefer.
Chop the red onion and fry it in a saucepan with a drizzle of olive oil.
Slice the mushrooms and add them to the onion and cook for 4 minutes. Set aside.
Preheat the oven (180°C).
Put the slices of cheese on the bread. Put the red onions and mushrooms mixture on top. Add the asparagus (eventually cut them in two lengthwise before).
Add salt, pepper and a hint of thyme.
Put in the oven for approx. 6 minutes until the cheese starts to melt.
Let it cool a bit before eating. When serving, add a few basil leaves on top and eventually a little bit of pesto.